A couple of suggestions:
The Emotiva CMX - http://hometheaterhifi.com/editorial/blogs/little-things-trouble-hum/

The Ebtech Hum Eliminators - http://www.ebtechaudio.com/hedes.html

Do you still have hum if you take the DSP out of the signal chain? If the hum does go away using an Ebtech HumX with the DSP should help.